1. Field of the Invention
The present invention relates to high resistivity silicon wafers for use of substrates of the high-frequency communication device and the like, in more particular relates to high resistivity silicon wafers for use of the base wafers of silicon wafers either having a silicon-on-insulator structure (SOI structure) or having an epitaxial structure, wherein mechanical properties are secured and the slip generation due to the heat treatment is suppressed, while no crystal originated particle (COP) exist therein.
2. Description of Related Arts
Since the high-frequency communication device for use of a near-field wireless LAN recently becomes common and/or gets micronized along with the growing number of signals, the demand for circuits commanding a high-frequency increases. And as high resistivity is required for substrates of high-frequency circuits, compound semiconductors such as GaAs and the like are conventionally used. However, substrates of compound semiconductors are very costly.
Meanwhile, in producing silicon single crystals by Czochralski method (referred to as “CZ method” hereinafter), raw materials are melted into molten liquid by using a quartz crucible and silicon single crystals are grown by directly pulling therefrom. Oxygen eluted from the quartz crucible while melting is resultantly contained in the crystal in supersaturated state. Consequently this oxygen contained in the crystal constitutes oxygen donors such as thermal donors and new donors in heat treatment step of device circuit fabrication process, and the resistivity of wafer is obliged to vary in device fabrication process.
Normally, in case of low resistivity wafers with about 10 Ω·cm of resistivity, the amount of dopants are abundant enough in comparison with the amount of generated oxygen donors, thereby the influence to the resistivity by generation of oxygen donors is exerted slightly. On the other hand, in case of high resistivity wafers, the amount of dopants is small, thereby its resistivity is severely affected.
Especially, in case of p-type, the electric conductivity resulted from positive holes by acceptors disappears due to the supply of electrons by donors and the resistivity increases markedly, whilst, as donors increase, the conversion to n-type semiconductors takes place, leading to the reduction of its resistivity. In another word, in p-type wafers, as the increase of oxygen donors goes on, its resistivity becomes very high in an early stage but further increase of oxygen donors causes the conversion from p-type to n-type, resulting in large reduction of the resistivity.
The amount of generated oxygen donors in general comes to small in silicon wafers with lowered oxygen concentration. Accordingly, in order to reduce oxygen content, there are disclosed methods for producing single crystals with low oxygen such as the magnetic field applied Czochralski method (MCZ method), which is to apply the magnetic field to silicon molten liquid in the crucible and pull single crystals while controlling the flow thereof, and the method for using quartz crucible of which the inner surface is coated with SiC, and the like.
Furthermore, there is a proposed method that, by using silicon wafers with low oxygen concentration to be obtained by virtue of inhibiting the dissolution of oxygen, the formation of oxygen donors such as thermal donors and new donors is restricted.
For instance, in the semiconductor device proposed by Japanese Patent Application Publication No. 2002-9081 is applied the method to process circuits onto substrates in which the concentration of interstitial oxygen (Oi) is 8×1017 cm−3 or less, the density of Bulk Micro Defect (BMD) is 1×108 cm−3 or more, and the specific resistance is 500 Ω·cm or more.
However, in fabricating these low oxygen concentration silicon wafers to be obtained by virtue of inhibiting the dissolution of oxygen, there arises problems such that there is technically a limit to further lower oxygen content, the cost thereof increases and further the strength of wafers reduces with lower oxygen, resulting in likely causing defective products due to the deformation of wafers in device processing stage.